I actually wanted to read all the post-release pages before contributing, but - not kidding - this thread is growing faster than I can read through it. So here are my thoughts, repetitive or not.
Crafting an ending for this series was always going to be tricky, but the way this one was handled came as a nasty surprise.
The choices presented to you are the result of a Deus ex Machina that, rather than feeling intriguing, undermines much of the mystique and the buildup of the trilogy thus far. Connections to the existing story arc(s) are tenuous, certainly not satisfyingly clear in the time you have to consider this new information and use it to choose a path. Instead of answers, more questions are created. There are problems leading up to the final choice.
Your actions over the entire trilogy are almost entirely inconsequential in determining possible outcomes. I expected failure. I expected various kinds of bittersweet. I hoped for hard-earned-but-worthwhile happy. What I didn't expect was a choice between three shades of galactic destruction. With what we have, the constraints on each choice that mean there is no single "best" choice (personally at least) feel somewhat arbitrary. For example, why does every choice result in the destruction of the mass relays? Considering the implications (destruction of each system if you go by Arrival's example, or at the very least a pronounced blow to the functioning of the galaxy), this is difficult to call a victory. The silliest thing is that the harder you work to rally more people to fight alongside you, the more that are left stranded in Sol away from their home systems. With some development, this ending could have been a thought-provoking option, but as the only option it is disconnected and bitter. There are problems with the choice itself.
It's been claimed these are multiple endings, and it's true that the options presented as they are would each have very different consequences. You, however, do not see any of them. Room for imagination is not a bad thing, but this seems to be a literal breaking of "show, don't tell". You are told, in a line or two, what will happen. You are shown a near-identical cutscene each time that adds nothing to your understanding of the choice you made and its consequences. Even putting aside the Normandy issue there is little exposition, no tying up of loose ends, no answering of questions, no real result of your entire journey. There is no closure. There are problems that persist even after the choice.
Sorry for the wall o' text, but I'm truly disappointed about this. I really would like to commend BioWare on crafting a fantastically immersive series, including this last game which I loved insanely until the ending, but it takes a special kind of botched job to destroy that good feeling in a matter of minutes at the end - to be honest I'm both amazed and appalled that it's produced the exact same reaction in so many people. If it turns out this is a joke on us - whether the indoctrination/hallucation theories are true or a "real ending" has been withheld - I find it in poor taste, because it means that the game is properly incomplete.
That said, I understand BioWare would need to tread carefully about it but I really, really hope we'll see a fix.
OK, back to lurking. Australian fleet out.